A commodity inspecting equipment such as a weighing conveyor for, while articles are successively transported by a conveyor apparatus in a production line, measuring the weight thereof includes, for example, a conveyor apparatus of a type in which an endless flat belt or the like is trained as a transport belt between a pair of rollers supported by a frame. One of the roller is a drive roller to which a driving force from a drive source such as a motor for moving the transport belt, and as a belt for transmission of the driving force an endless belt or the like is trained between a pulley, mounted coaxially on the drive roller, and a pulley mounted on a drive shaft of the drive source.
The conveyor apparatus is coupled with a free end side of an elastic element so that it can serve as a load to a load cell as a load detector. A fixed end side of the elastic element is coupled with a fixed member such as a leg member, a fixed frame, a fixed bracket or the like. The load cell is generally accommodated within a housing so that it will not be affected by an external environment such as moisture, dusts and others.
A relation in position between the conveyor apparatus and the housing is such that since a space above the conveyor apparatus is required to be open wide in view of articles to be weighed being placed on the conveyor apparatus and since measurements would result in an error when foreign matter falls onto the conveyor apparatus, the conveyor apparatus is generally disposed immediately above the housing or in side by side fashion relative to the housing. Accordingly, hitherto, the housing has an opening defined on a top surface or a side surface, and a support member for the support of the conveyor apparatus is passed through the opening so as to extend outwardly from the top surface or side surface of the housing. One end side of the support member is connected with the free end side of the elastic element, whereas the other end side thereof extends upwardly or laterally towards the conveyor apparatus, and the opening through which the support member extends is closed by a diaphragm.
In the meantime, this type of the weighing conveyor is sometime used for transport and weighing of food materials and, in such case, a water component and/or dregs of the food materials may fall and/or scatter onto the housing to deposit on surfaces of the housing. However, if the top surface or side surface of the housing has the opening through which the support member extends and the diaphragm or the like, the dregs deposited thereon tend to easily accumulate, resulting in proliferation of unwanted bacteria to such an extent as to result in degradation of sanitary conditions and also to perforation in the diaphragm as a result of the dregs or the like having been bitten. Also, even where a cleaning work is regularly performed using a cleansing liquid or the like, a surface structure of the top surface or side surface of the housing is complicated, resulting in the cleaning capability of the opening, diaphragm and their surroundings being reduced.
As a technique capable of dealing with the foregoing problems, there is what is disclosed in the Japanese Laid-open Patent Publication No. 9-297051. This technique is such that while the load cell is accommodated within a housing, a member for connecting a fixed end portion of an elastic element to a fixed member external to the housing is passed from a lower surface of the housing to the outside. By so doing, neither the opening nor the diaphragm is positioned above the top surface or side surface of the housing, resulting in improvement in capability of being cleaned.
However, in the technique disclosed in the above mentioned publication, the fixed end portion of the elastic element is connected with the fixed member external to the housing and the free end portion is connected with the housing. Also, a support member is mounted on a surface of the housing and the conveyor apparatus is supported by the housing. Accordingly, in addition to the weight of the conveyor apparatus, the weight of the support member or the weight of a drive transmission mechanism, such as the drive motor, the drive transmitting belt and pulleys or the like, the weight of the housing is loaded on the load cell as a tare weight and, therefore, the tare weight tends to become heavy, accompanied by reduction in natural frequency of a measurement system of the weighing conveyor, which in turn results in lowering of the weighing accuracy.
Also, in this weighing conveyor, the drive shaft of the drive motor extend in a direction perpendicular to the direction in which the elastic element of the load cell displaces upon receipt of a load. For this reason, the direction in which a portion of the centrifugal force generated as a result of rotation of the drive shaft acts coincides with the above mentioned direction of displacement of the elastic element. Accordingly, there has been a problem in that a weight signal outputted from the load cell contains noises and, therefore, the weighing accuracy tends to be lowered.
On the other hand, since the load cell is downwardly loaded with a load of the articles by the effect of a gravitational force, the direction in which the elastic element displaces during a load detection lie in a direction up and down. In other words, hitherto, in this type of the weighing conveyor, a transport surface of the conveyor apparatus lies perpendicular to the direction of displacement of the elastic element and the longitudinal axis of the drive shaft of the drive source lie parallel to the transport surface of the conveyor apparatus.
In view of the foregoing, in the event that a centrifugal force is generated as a result of rotation of the drive shaft of the drive source, accompanied by the generation of vibration, a portion of the direction of the vibration induced by the centrifugal force acts also in a direction up and down. Since the up and down direction lie in the direction in which the elastic element of the load cell displaces during the load detection, a change in load brought about by the vibrations is detected by the load cell, with the consequence that the weight signal from the load cell contains noises, resulting in reduction of the weighing accuracy.
The more considerable the fluctuation of the drive shaft being driven, the more considerable the vibration brought about by the effect of the centrifugal force. In other words, in the event that the mass of the rotating element is in an unbalanced state with respect to the center of rotation thereof or the drive shaft fluctuate about the longitudinal axis thereof during rotation thereof, the noises tend to become paramount.
In order to alleviate the above discussed problems, a technique disclosed in, for example, the Japanese Laid-open Patent Publication No. 8-136330 may be employed. In other words, in addition to a first standard load cell displaceable up and down to detect the weight of an article to be weighed, a second load cell is used and operable to displace in a horizontal direction parallel to a direction of transport. This second load cell is used to detect a vibration acting in the transport direction as a result of rotation of a rotary element. Since the vibration generated therein is a centrifugal force, it has an equal magnitude in all directions within a plane perpendicular to a plane of transport. Accordingly, by subtracting the vibration detected by the second load cell from a weight signal detected by the first load cell after the phase relationship between them has been rectified, noises resulting from the vibration can be eliminated.
However, with the known technique, plural load cells are required and, accordingly, not only does a hardware aspect become complicated, but also a software aspect of a signal processing for processing the weight signal becomes complicated, resulting in disadvantages in terms of cost. In view of this, there is a need to simplify the structure enough to avoid reduction in weighing accuracy which would otherwise results from containment of noises in the weight signal outputted from a load detector as a result of a rotatory vibration of the drive source.
Also, in this type of weighing conveyor, since the load cell, the drive motor and the drive transmission mechanism are all disposed between upper and lower runs of the transport belt, the conveyor apparatus tends to have an increased size particularly a heightwise direction thereof. Accordingly, since the natural frequency of the weighing conveyor decreases as a result of increase of the weight of the conveyor apparatus, that is, the tare weight, a low pass filter having a high cutoff frequency, for example, cannot be used. For this reason, the response of the filter does not increase so much and a filter processing time does not decrease so much, and accordingly, a high speed weighing operation is hampered.
Accordingly, the present invention has been devised in view of the foregoing problems and is intended to increase the accuracy of inspection including the weighing accuracy. Hereinafter, the present invention will be described in detail, including the underlying problems.